Service Workers is a key tool for implementing offline functions and caches of web pages. It runs in the browser background, is independent of the main thread, can intercept network requests and manage caches, and is the core technology for building PWA. 1. Service Worker is a background script that does not operate the DOM directly. It supports push notifications, background synchronization and other functions. It only runs in the HTTPS environment (except for the development environment). Its life cycle includes the registration, installation and activation stages. 2. To register a Service Worker, you need to call the register method in the main JS file, specify the script path and listen to the registration results. 3. Use the Cache API to cache critical resources during the installation phase and prioritize cached content in the fetch event. 4. To optimize offline experience, different caching strategies can be set, such as HTML adopts network priority, image adopts cache priority, and offline pages can be cached as a guarantee solution. 5. Cache strategies should be carefully designed when using them, avoid full cache or completely bypassing caches, and pay attention to version management and cache cleaning to prevent old caches from affecting debugging and updates.

Want your web page to be used when it is disconnected? Service Workers are a key tool for implementing offline functionality and caching. It is like a background proxy, allowing you to control page resource loading, cache policies, and even return cached content when there is no network.

Here are some practical points you may be concerned about:

What is Service Worker?

Service Worker is a script running in the browser background, independent of the main thread and does not operate the DOM directly. It can intercept network requests and manage caches, and is one of the core technologies for implementing PWA (progressive web application).

It has several characteristics:

• Support advanced functions such as push notifications, background synchronization, etc.
• Run only under HTTPS (except for development environments)
• Life cycle independent, requires registration and activation

How to register a Service Worker?

To enable Service Worker on a web page, you must first register it in the main JavaScript file:

 if ('serviceWorker' in navigator) {
  navigator.serviceWorker.register('/service-worker.js')
    .then(registration => {
      console.log('Service Worker registration successfully', registration);
    })
    .catch(error => {
      console.log('Register failed:', error);
    });
}

A few notes:

• service-worker.js is the Service Worker script you wrote
• It is recommended to place it in the website root directory so that it can control the entire site
• After successful registration, the browser will automatically install and activate it

How to use Service Worker for caching?

Service Worker provides a Cache API that allows you to manually cache resources. It is common practice to cache key resources during the installation phase and then return cached contents when requested.

A basic caching strategy:

 const CACHE_NAME = 'my-cache-v1';
const urlsToCache = [
  '/',
  '/styles/main.css',
  '/scripts/app.js'
];

self.addEventListener('install', event => {
  event.waitUntil(
    caches.open(CACHE_NAME)
      .then(cache => cache.addAll(urlsToCache))
  );
});

self.addEventListener('fetch', event => {
  event.respondWith(
    caches.match(event.request)
      .then(response => response || fetch(event.request))
  );
});

In this example:

• The specified resources are cached during the installation phase
• Each request will check the cache first
• If the cache is not available, go to the network to request

How to optimize offline experience?

Caching resources alone are not enough, you have to consider the user's experience when the Internet is really out of the network. for example:

• Caches a "offline page" and returns it when all attempts fail
• Use the Network First or Cache First policies to handle flexibly based on resource type

For example: You want HTML pages to be loaded from the network first, but images are cached first:

 self.addEventListener('fetch', event => {
  const request = event.request;

  // HTML request network priority if (request.headers.get('Accept').includes('text/html')) {
    event.respondWith(
      fetch(request)
        .catch(() => caches.match(request))
    );
  }

  // Image cache priority if (request.destination === 'image') {
    event.respondWith(
      caches.match(request)
        .then(response => response || fetch(request))
    );
  }
});

Service Worker is powerful but requires careful use. The cache strategy should be determined based on the business. Don’t cache it all, and don’t go to the Internet every time. When updating Service Worker, you should also pay attention to version control and cache cleaning, otherwise the old cache may cause you to debug to crash.

Basically all is it, not complicated but it is easy to ignore details.

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